dmaengine: pch_dma: remove unused function chan2parent

The helper function chan2parent is not used and has never been
used since the first commit to the code back in 2010. The function
is redundant and can be removed.

Cleans up clang scan build warning:
drivers/dma/pch_dma.c:158:30: warning: unused function 'chan2parent' [-Wunused-function]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20240308134750.2058556-1-colin.i.king@gmail.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>